“Donte Walker was responsible for bringing this gun into the school,” says Lt. Stanford.

Over the weekend, investigators discovered additional video showing what appears to be Walker exchanging cash for a black handgun and entering Delaware Valley Charter High (see previous story).

Police say Walker’s status as a former student allowed him to get around a security checkpoint with metal detectors.

“By him being a former student, he’s considered a guest. So there’s a good possibility that he didn’t have to go through the metal detectors,” explains Lt. Stanford.

The gun ends up with Rochwell after another exchange.

Police say a single shot was fired around 3:30 p.m. in the school gym. A single bullet struck a female student and a male student on the arm and the shoulder.

“I can’t see why you would allow anybody else – visitor, former student, anyone – to enter school without having to go through the same protocol [as everyone else],” Stanford says.

On Monday, Delaware Valley Charter released a letter to the school community that read in part:

“It is with a heavy heart that we have to confirm that on Friday, January 17, 2014, two students were wounded by gunfire in the school’s gymnasium. We know that in a world of increased violence, occurrences such as these have been in the public consciousness. However, it is very disconcerting to have it happen in our own community. While saddened by these series of events, the administration and board are even more committed to providing a safe and quality learning environment for the school’s students and staff.”

The school also announced that although it will be operating on a regular schedule on Tuesday, students are encouraged to arrive at 7:30 a.m. to allow for adequate time to get through the tightened security measures in place.

“In addition to a thorough review of measures within the school to protect students and staff, the administration and board will continue to be in full cooperation with the Philadelphia Police Department as its investigation continues,” Delaware Valley Charter said.

So far, investigators say the shooting is likely an accident, and they are calling for change.

“It’s something that has to be corrected in terms of their safety protocol of allowing people to enter [the school] without going through metal detectors,” Lt. Stanford says.